For example, JP-2004-333133 A (Patent Document 1) and U.S. Pat. No. 6,936,491 (Patent Document 2) each disclose a semiconductor device and its manufacturing method in which a sealing cap is provided for each of various elements formed on a surface layer of a semiconductor base substrate so as to protect the elements.
FIGS. 26A and 26B show a semiconductor device (inertia force sensor) disclosed in Patent Document 1. FIG. 26A is a top view of the inertia force sensor. FIG. 26B is a cross sectional view taken in the line XXVIB-XXVIB of FIG. 26A. In the following description, a horizontal direction in FIGS. 26A and 26B is assumed to be “lateral.” A direction perpendicular to the lateral direction is assumed to be “longitudinal.”
The inertia force sensor in FIGS. 26A and 26B is provided with a device layer 11. The device layer is formed integrally with a spring 1, an anchor 2, a beam 3, a mass unit 4, island electrodes 7a and 7b, and a frame 10. A bottom substrate 12 and a top substrate 13 are respectively bonded to bottom and top surfaces of the device layer 11. The device layer 11 is sealed between the substrates 12 and 13.
The island electrode 7a (electrode for movable electrode) electrically connects a movable electrode 5 to the outside. The island electrode 7b (electrode for fixed electrode) electrically connects a fixed electrode 6 to the outside. Top surfaces of the island electrodes 7a and 7b are provided with electrode pads 8 for electrical connection with external devices. The top substrate 13 is provided with through holes 9 corresponding to the electrode pads 8. The electrode pads 8 are exposed outward. Though not shown, the electrode pads 8 are electrically connected to external ICs etc. via wire bonding through the through holes 9.
On the inertia force sensor as shown in FIGS. 26A and 26B, the anchor 2 is fixed (bonded) to the bottom substrate 12. The island electrodes 7a and 7b and the frame 10 are fixed (bonded) to the substrates 12 and 13. The spring 1, the beam 3, and the mass unit 4 are not connected to the substrates 12 and 13. Each beam 3 is supported by the corresponding anchor 2. The mass unit 4 is supported by two beams 3 laterally and displaceably. The spring 1 correspondingly connects the anchor 2 with the island electrode 7a. The spring 1 also connects the anchor 2 with the island electrode 7a electrically.
When viewed longitudinally, both sides of the mass unit 4 are provided with the movable electrodes 5. The fixed electrode 6 is provided for the island electrode 7b for fixed electrode. At both sides of the mass unit 4, the movable electrode 5 and the fixed electrode 6 laterally face to each other. When an inertia force is laterally applied to the inertia force sensor, the inertia force laterally moves the mass unit 4 and changes the lateral position relationship (interval) between the movable electrode 5 and the fixed electrode 6. Changing the interval also changes a capacitance between the movable electrode 5 and the fixed electrode 6. A capacitance change can be used to detect the inertia force applied to the inertia force sensor.
The inertia force sensor in FIGS. 26A and 26B uses the island electrodes 7a and 7b that are electrically insulated from each other. The movable electrode 5 provided for the mass unit 4 is electrically connected to the island electrode 7a for movable electrode via the beam 3, the anchor 2, and the spring 1 in order. The island electrode 7a is electrically connected to an external IC etc. via the electrode pad 8 on the top surface of the island electrode 7a and the wire bonding (not shown) through the through hole 9. The fixed electrode 6 for fixed electrode is provided for the island electrode 7b. The fixed electrode 6 is electrically connected to an external IC or elsewhere via the island electrode 7b, the electrode pad 8 thereon, and the wire bonding (not shown) through the through hole 9.
As mentioned above, the inertia force sensor in FIGS. 26A and 26B uses the wire bonding to the electrode pads 8 on the island electrodes 7a and 7b via the through holes 9 in the top substrate 13 for electrical connection to an external IC etc. However, the wire bonding requires the through hole 9 large enough for a bonding tool to avoid contact with the top substrate 13. The chip size accordingly increases to cause a cost problem. As seen from FIG. 26B, the above-mentioned structure makes face down bonding (ball bonding) difficult, causing mounting restrictions.
Thus, It is required for a semiconductor device in which a sealing cap is provided for various elements formed on a surface layer of a semiconductor base substrate so as to protect the elements, inexpensively manufacture a small device, enable face down bonding, and reduce mounting restrictions.